Enable loads and stores to global vars through property cell shortcuts...

Enable loads and stores to global vars through property cell shortcuts installed into parent script context.

Review URL: https://codereview.chromium.org/1237603002

Cr-Commit-Position: refs/heads/master@{#29595}

src/flag-definitions.h

@@ -665,7 +665,7 @@ DEFINE_BOOL(use_idle_notification, true,
 DEFINE_BOOL(use_ic, true, "use inline caching")
 DEFINE_BOOL(trace_ic, false, "trace inline cache state transitions")
 DEFINE_BOOL(vector_stores, false, "use vectors for store ics")
-DEFINE_BOOL(global_var_shortcuts, false, "use ic-less global loads and stores")
+DEFINE_BOOL(global_var_shortcuts, true, "use ic-less global loads and stores")
 
 // macro-assembler-ia32.cc
 DEFINE_BOOL(native_code_counters, false,